Detectives investigating a stabbing in a park in Pinner have arrested four people on suspicion of attempted murder.
The arrests were made on Saturday, 29 August and Sunday, 30 August.
Two men aged 22 and 24, and two teenage boys, both aged 15 remain in police custody.
The incident is believed to have happened at about 6.05pm on Wednesday, 26 August in Montesole Playing Fields.
Officers and London Ambulance Service were called to reports of a person stabbed in the park and found an 18-year-old man with a stab wound.
London’s Air Ambulance attended the scene and the man was taken to hospital.
He currently remains in hospital in a critical condition. His next of kin are aware and are being supported by officers.
The inquiry is being led by detectives from the North West Command Unit, who continue to appeal for information.
BCU Commander for North West London, Roy Smith, said: “I know that local communities will have been shocked by this attack and would like to reassure them that we are not currently looking for any other suspects.
“I’m grateful to the members of the public who have come forward with information already to assist our investigation and local officers will continue to provide additional patrols in the park and surrounding area.”
Any witnesses or anyone with any information is asked to call police on 101 or contact via Twitter @MetCC. Please quote CAD 5906/26AUG.